Auto Loan Amortization Schedule Calculator

An auto loan amortization schedule shows how each monthly payment is split between interest and principal, and how the balance declines over time. Enter the amount financed, annual percentage rate (APR), and term to estimate the monthly payment and total interest; the schedule itself can be built by applying the same monthly calculation to each payment.

Formula

The calculator uses a fixed-payment, fully amortizing loan formula. It computes the unrounded payment from the principal and monthly rate, then displays the payment to the nearest cent. Total interest is calculated using that displayed, cent-rounded payment for every scheduled month.

• Monthly rate: r = APR / 1,200, where APR is entered as a percentage per year and r is the monthly decimal rate.
• Number of payments: n = years × 12.
• Monthly payment: M = round to cents of P × r / [1 − (1 + r)⁻ⁿ].
• Total interest: I = M × n − P.

P is the amount financed in dollars, M is the monthly payment in dollars, and I is total scheduled interest in dollars. The calculator’s formula assumes the loan is repaid through equal monthly payments. The final payment on an actual loan may differ slightly because lenders can calculate daily interest, adjust for payment dates, or handle rounding differently.

Worked Example

Using the calculator’s defaults: P = $20,000, APR = 8%, and term = 5 years.

1. Convert the APR to a monthly rate: r = 8 / 1,200 = 0.0066667, or about 0.66667% per month.
2. Find the payment count: n = 5 × 12 = 60 months.
3. Apply the payment formula: M = $20,000 × 0.0066667 / [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month after rounding to cents.
4. Calculate total scheduled payments: $405.53 × 60 = $24,331.80.
5. Subtract the amount financed: $24,331.80 − $20,000 = $4,331.80 total interest.

The monthly payment is the headline result; the interest figure is the total across the scheduled payments under the stated assumptions.

Assumptions

• The interest rate stays fixed for the full term.
• Payments are level monthly payments, made at the end of each monthly period.
• Interest compounds monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, and other amounts unless they are included in the amount financed. It does not model optional products or changing payment dates.

How to Read an Auto Loan Schedule

A full amortization schedule has one row per payment. Common columns include the payment number or date, payment amount, interest charged, principal repaid, and remaining balance. To make each row, multiply the balance at the start of that month by the monthly rate to estimate interest. Subtract that interest from the payment to find the principal portion, then subtract the principal portion from the old balance.

For example, on the first month of the default example, estimated interest is $20,000 × 0.0066667, or about $133.33. From a $405.53 payment, about $272.20 goes toward principal, leaving an estimated balance of $19,727.80. Later, interest is calculated on the smaller remaining balance, so more of a level payment generally goes to principal as the loan progresses. A real lender’s schedule may vary by a few cents due to its calculation and rounding method.

The displayed total interest is not an extra charge added to the monthly payment; it is the sum of the interest portions across the planned payments. The amount financed is also not necessarily the vehicle’s advertised price: it may reflect a down payment, trade-in credit, or eligible charges rolled into the loan. Use the amount actually financed from the loan paperwork when available.

What Changes the Payment and Interest

For the same amount financed and APR, a longer term spreads repayment across more months. That usually lowers the scheduled monthly payment but increases the number of months in which interest accrues, which can raise total interest. A shorter term has fewer payments and generally less total interest under this formula, while its monthly payment is higher. These are mathematical effects, not a judgment about which loan to choose.

The APR and amount financed also matter. A higher APR increases the monthly interest rate used in each balance calculation. Adding amounts to the financed balance increases the principal on which interest is calculated. The calculator uses the APR and amount as inputs; it does not determine a rate, estimate lender charges, or establish a borrower’s eligibility. Get the exact APR, amount financed, payment dates, and disclosed payment amount from the lender’s documents.

Using the Estimate and Common Pitfalls

• Enter the financed amount, not automatically the vehicle price. A down payment or trade-in can make the loan principal different from the purchase price.
• Enter APR as a percentage per year. For example, enter 8 for 8%, not 0.08. The formula divides by 1,200 to convert it to a monthly decimal rate.
• Keep the term in years in this calculator. It converts years to months by multiplying by 12. A term stated in months must first be converted accurately.
• Expect rounding differences. A lender may use daily simple interest, exact dates, or a different rounding process. The estimate applies a level monthly payment and cent rounding.
• Account for the whole ownership budget separately. The calculator does not include insurance, fuel, maintenance, registration, or other costs of having a vehicle.

An amortization schedule is useful for understanding the planned balance at each point and for checking how principal and interest are allocated. It is not a payoff quote: paying off a loan early can require a date-specific interest calculation and account for amounts or adjustments that this model does not include. Extra payments are not reflected in the fixed-payment result, so a schedule with extra principal payments would need to recalculate the balance after each payment.

Frequently Asked Questions

What is an auto loan amortization schedule?
An amortization schedule is a payment-by-payment breakdown of a loan. It shows how much of each payment is assigned to interest and principal and the estimated balance remaining afterward.

How do I calculate interest for one month?
Multiply the balance at the beginning of the month by the monthly rate. With an APR expressed as a percentage, the simple monthly-rate conversion used here is APR ÷ 1,200. A lender may use a different method, including daily interest.

Why does more of the payment go to principal later?
With a fixed payment and declining balance, the interest portion generally gets smaller over time. The amount left from the payment after interest is applied therefore generally becomes a larger principal reduction.

Does a longer auto loan term reduce total interest?
Not under the same amount financed and APR in this fixed-rate model. A longer term usually reduces the scheduled monthly payment but adds payment periods, which generally increases total interest.

Is the calculator’s total interest an exact payoff amount?
No. It is estimated interest over the scheduled term using fixed monthly payments and the stated assumptions. A payoff amount can depend on the actual balance, payment timing, lender calculations, and other account details.

The result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• US Interest Rate: What It Means and How It Works
• Interest Rate Tracker: Estimate Payments and Interest
• Interest Rate Trends: How Rates Change Over Time

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2